JPS5923490A - Induction heating cooking device - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an induction heating cooker with an added function of suppressing fluctuations in current peak values of switching elements constituting an inverter.

Commercial AC power supplies usually have voltage fluctuations of about ±10%. This voltage variation affects the oscillation current of the inverter, causing it to vary at approximately the same rate. For example, switching elements constituting an inverter, such as GTO, are designed so that a peak current of about 60 A flows at a normal power supply voltage, but when the power supply voltage increases, the value increases to about 64 A. When turning off switching elements such as C2, it is impossible to turn them off unless an off current proportional to the magnitude of the current flowing between the anode and cathode or between the emitter and collector is applied to the gate or base. Therefore, if the anode-cathode current or emitter-collector current changes, the gate current must change the base current accordingly.
Although it is not impossible to provide the driving circuit of the switching element with such a driving/magnetic current changing function, it requires a complicated circuit configuration, and considering cost etc., it is difficult to actually install it in this type of cooker. Furthermore, if the switching element current changes in response to fluctuations in the power supply voltage, the input to the load (= applied input) also changes at approximately the same rate, resulting in the disadvantage that the set power is not accurately applied to the load.

The present invention suppresses fluctuations in the peak value of the current flowing through the switching element f even when the power supply voltage fluctuates.

The purpose is to stabilize this value. That is, one aspect of the present invention is to detect the voltage, and when the voltage increases, to shorten the conduction period of the switching element accordingly, thereby suppressing the peak current.

Examples of the present invention will be described below.

In FIG. 1, (11 is a commercial AC power supply, 121 is a power switch, (3) is a rectifier circuit, (4) is a choke coil, (5) is a filter capacitor, and (61 is an inverter.

A series resonant circuit consisting of an induction heating coil (7) and a resonant capacitor (8), a switching element such as GTOi91 and a diode (101) connected in parallel to the resonant capacitor (8). 011 is a filter capacitor (5)
Terminal that obtains the pulsating power supply voltage ■0 obtained from the terminal, tJ2c, G T 0i91 (7) 7/ -)
'i [pressure V k': obtained; 6 terminals. G T O+
A drive signal VG is applied to the gate of 91 to control the oscillation of the inverter (6).

A stainless steel copper plate is placed on the induction heating coil (7) via a top plate. 1131 is a lance for detecting input current, and its voltage conversion output is expressed in VOT.

FIG. 2 shows a control part that continues the oscillation of the inverter (6) at an arbitrary frequency, and the input current detection signal VOT is
It is rectified by the rectifier circuit 041, and the smoothing capacitor [15+
The smoothed signal is input to the e input terminal of the comparator 061.

A signal of a predetermined level obtained by dividing the constant voltage CO by a resistor (+71) and a variable resistor is given to the input terminal of this comparator marked 0.The variable resistor 0 & outputs a signal containing the input image level. Smoothed with condenser fo!l, G TO
A signal Von for turning on 191 is applied to the 0 input terminal of the comparator. Reference numeral 121+ denotes a flip-flop whose reset terminal receives the output of the comparator (1), and its set output Q is applied to the G'I'O drive circuit Cchi2. And when the set output Q is at H level, G
From T O drive circuit prisoner.

When the GTO on signal is again at L level, the GT
An O off signal is output. Note that this is an L flip-flop.

The illumination voltage VO is divided by the resistor (241) and inputted to the O input terminal C of the comparator G. The constant voltage voa is divided by the resistor (2η) and the variable resistor (281
A predetermined signal divided at is added. The output v1 of the comparator is smoothed by a capacitor V-1-12' (signal Vg) and applied to a transistor 3 and a capacitor (2) via a resistor (2). The terminal voltage of the capacitor (2) is a signal for generating a GTO off signal, Vof
It is input as f to the e input terminal of comparator 12+male. The pace of the transistor cIυ [the second is the flip-flop C2
The reset output Q of II is added.

The anode terminal voltage VA of G T O+91 is applied to the e input terminal of the comparator. The output v2 is differentiated (signal V5) through a differentiating circuit consisting of a capacitor and a resistor (b), then inverted (signal VFl) by an inverter (to), and input to the set terminal of flip-flop L21I. In the same sentence, the input current detection signal VOT is
The voltage VO is used as an input current detection signal and as a signal for countermeasures against power supply voltage fluctuations.

Next, the operation will be explained using FIGS. 3 to 5. Third
Period T2 in the figure indicates that the power supply voltage is normal.
indicates the case where the power supply voltage increases.

The power supply detection signal VOT is rectified and Wm is sent to the comparator 11θ.
Enter. Since the power level of the comparator 111 is arbitrarily set by the input adjusting variable resistor U+knee, its output C2 becomes a rectangular wave with a longer h level period as the input power increases. This square wave is the capacitor u
1 and converted into a voltage level signal Von. Therefore, the level of this signal Von will respond to human power (2).

On the other hand, the power supply voltage (2)0 is input to a comparator and is compared with a predetermined θλ voltage level to output a rectangular wave signal V1 which is longer in period T2 than in T1. This signal v1 is smoothed by the capacitor 21 (vE) and further charged into the capacitor (tVo//) when the transistor 6D is turned off.

Periods t1 and t2 in FIG. 4 are temporally expanded portions of periods T+ and Tt in FIG. When the flip-flop circuit is set by a set signal VB, which will be described later, the transistor 6η is turned off by the set cassette output of the flip-flop &11, and therefore charging of the capacitor (2) is started, and this voltage Vo
When ff reaches the signal VOnr2, the comparator is reset. From the inversion C2 of this flip-flop αB, the reset output is enabled 'AH#, and the transistor 8υ turns on.
The charge on the capacitor is immediately discharged.

Therefore, the output Vn of comparator (2) becomes an L level pulse. Period t! Since the value of the voltage vB' is larger than the period, the charging time of the capacitor becomes faster and the rising angle of the voltage VO becomes steeper. Therefore, the time required to reach the voltage VOn is shortened, and the set period of the flip-flop +211 is shortened. That is, flip-flop 2 in period 1i Jitt, tz
The relationship between the set periods ta and tb in No. 11 is r, a:>tb, and the difference is proportional to the difference in power supply voltage VC. In this way, when the power supply voltage rises f2, the set output period of the flip-flop 4 is shortened, that is, the on period of the GTOi 91 is shortened, and the peak value of the current flowing between the anode and cathode is suppressed. Actually, the current peak value is FJ6
When set to DA, regardless of voltage fluctuation C2,
It was confirmed that the value could be stabilized.

FIG. 5 shows the set signal VB of the flip-flop f21+.
G
The TO anode voltage VA and the divided voltage of the voltage VO are compared, and the pulse signal V is outputted at the rising edge of the signal 2 when the voltage VA is approximately zero.

As described above, the induction heating cooker of the present invention detects fluctuations in the power supply voltage, and when this voltage increases.

Since the ON period of the switching element is shortened by a time proportional to the increase, it is possible to prevent a current exceeding a set value from flowing through the switching element, and to stabilize the current. So.

As a result, it is possible to use a constant current signal as an off signal for the switching element, and the driving circuit for the switching element can be simplified. Furthermore, the input power applied to the load can be maintained at a set value regardless of fluctuations in the power supply voltage.

[Brief explanation of drawings]

Figures 1 and 2 are circuit diagrams of an embodiment of the present invention, and Figures 3 to 5 are waveform diagrams of operating signals on the same side.(6)...Inverter (7)...Induction heating coil ( 8)・
...Resonance coVden f(9)...GTOQl...Diode 031...Current transformer αto...
Flip-flop Shima...GTO drive circuit: ``t-to-ku oc''
L12 To ■ To To To
Toku νtsu faction

Claims (1)

[Claims] t In an induction heating cooker having a power supply, a series circuit consisting of an induction heating coil and a resonant capacitor, and an inverter including at least a switching element connected in parallel to the resonant capacitor, detecting the terminal voltage of the power supply and responding to an increase in this voltage. An induction heating cooker characterized in that it is provided with conduction period control means for shortening the conduction period of the switching element.